hmmm

Yeah they usually have a chip in them tho. If the voltage gets below a threshold, the chip disconnects the cells from the output. The idea is the cells are probably damaged beyond recovery at that point and attempting to use or charge them is a fire risk.

But another result is when people replace the cells, the battery still won't work. And because right to repair laws are still a joke, the people making either the tools or the batteries don't release any documentation about what chip is used or if/how it can be reset once new cells are inserted.

I had a pretty nifty cordless vacuum cleaner which had a battery built in. The battery wore out, so I looked into replacing it. But it was a nightmare. All plastic clips that broke when trying to get stuff apart. A ton of hidden screws and the worst part: the cells were all encased in a lot of plastic, a tape like stuff and what looked like epoxy. Plus the connections were spot welded. In the end I gave up and bought a new corded one. A waste to replace something that could have been repaired, had it not been terribly made. The new corded one will last longer I hope and at least remain at max power till it dies.